Behavioral inferences from regulatory observer data: catch rate variation in the Scotian Shelf silver hake (Merluccius bilinearis) fishery

1999 ◽  
Vol 56 (2) ◽  
pp. 288-296 ◽  
Author(s):  
D M Gillis
Keyword(s):  
Interference Competition ◽  
Temporal Trends ◽  
Catch Rate ◽  
Rate Variation ◽  
Scotian Shelf ◽  
Apparent Contradiction ◽  
Fishing Vessels ◽  
Catch Rates ◽  
Silver Hake ◽  
Merluccius Bilinearis

The detailed spatial and temporal data collected for the regulation of the silver hake (Merluccius bilinearis) fishery on the Scotian Shelf provide a unique opportunity to test hypotheses about variability in catch rates on the scale of individual trawls. I used these data to examine vessel interactions and long-term temporal trends in catchability. An index of course linearity, derived from observed positions, times, and speeds of fishing vessels, indicated that interference competition was present in the fishery. However, catch rate did not decline with local vessel density. This apparent contradiction is consistent with fleet dynamic theory and suggests that the direct examination of catch rates is a poor test for interference in the retrospective analysis of fisheries data. The study of extended periods of high, localized fishing activity revealed a cycle in catch rates with periods of about 6 days. Such periods may represent an interaction between tidal, diel, and (or) technological factors. Although more study is required to identify the cause of these cycles, their existence should be considered in the design of surveys and other population studies using catch and effort data.

An "experiment" on effort allocation of fishing vessels: the role of interference competition and area specialization

2007 ◽  
Vol 64 (2) ◽  
pp. 304-313 ◽  
Author(s):  
Jan-Jaap Poos ◽  
Adriaan D Rijnsdorp
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Seasonal Pattern ◽  
Interference Competition ◽  
Catch Rate ◽  
The North ◽  
Closed Area ◽  
Fishing Vessels ◽  
The North Sea

A temporarily closed area established to protect spawning Atlantic cod (Gadus morhua) in the North Sea allowed us to study the response of the Dutch beam trawl fleet exploiting common sole (Solea solea) and plaice (Pleuronectes platessa). A number of vessels left the North Sea 1 month earlier than the normal seasonal pattern. The vessels that continued fishing in the North Sea were concentrated in the remaining open areas. In the first week after the closure, the catch rate decreased by 14%, coinciding with an increase in crowding of 28%. Area specialisation affected the response of individual vessels because vessels without prior experience in the open areas showed a larger decline in catch rate compared with vessels that previously fished in these open areas and were more likely to stop fishing during the closed period. The decrease in catch rate in response to the increase in competitor density allowed us to estimate the strength of the interference competition.

scholarly journals Response of Scotian Shelf silver hake (Merluccius bilinearis) to environmental variability

2018 ◽  
Vol 28 (3) ◽  
pp. 256-272 ◽  
Author(s):  
Daniel Reed ◽  
Stéphane Plourde ◽  
Adam Cook ◽  
Pierre Pepin ◽  
Benoit Casault ◽  
...  
Keyword(s):  
Environmental Variability ◽  
Scotian Shelf ◽  
Silver Hake ◽  
Merluccius Bilinearis

Growth variation and water mass associations of larval silver hake (Merluccius bilinearis) on the Scotian Shelf

2000 ◽  
Vol 57 (8) ◽  
pp. 1728-1738 ◽  
Author(s):  
Jennifer A Jeffrey ◽  
Christopher T Taggart
Keyword(s):  
Water Mass ◽  
Age And Growth ◽  
Scotian Shelf ◽  
Growth And Survival ◽  
Growth Variability ◽  
Wet Biomass ◽  
Growth Variation ◽  
Silver Hake ◽  
Age Relations ◽  
Merluccius Bilinearis

Otolith microstructure is shown to be ideal for assessing age and growth in silver hake (Merluccius bilinearis) larvae and is used to examine growth among individuals and cohorts. Larvae collected from Western Bank, Scotian Shelf, in September, October, and November 1997 defined three monthly cohorts identified using inferred hatch dates. Total length-at-age relations did not differ between the September and October cohorts despite substantial differences in growing degree-day (435 versus 318°C·d) and zooplankton (potential prey index) wet biomass (0.15 versus 0.27 g·m-3). Larvae collected off-bank in September exhibited a growth advantage of >0.10 mm·d-1 relative to larvae collected on-bank. Greater variability in growth rate within cohorts and among water masses implies that cohort-averaged growth and survival (based on growth) estimates can be biased by overrepresentation of a single water mass. The focus on growth variability, and its relationship to survival, should be on individuals within cohorts and not on cohort-averaged estimates. We hypothesize that growth, and perhaps survival, in silver hake larvae on the Scotian Shelf is most easily explained by variation in physical oceanographic processes.

scholarly journals Reduced herding of flounders by floating bridles: application in Gulf of Maine Northern shrimp trawls to reduce bycatch

2014 ◽  
Vol 72 (5) ◽  
pp. 1514-1524 ◽  
Author(s):  
Pingguo He ◽  
Christopher Rillahan ◽  
Vincent Balzano
Keyword(s):  
North Atlantic ◽  
Gulf Of Maine ◽  
Shrimp Fishery ◽  
The North ◽  
Northern Shrimp ◽  
Shrimp Fisheries ◽  
The Difference ◽  
Catch Rates ◽  
Silver Hake ◽  
Merluccius Bilinearis

Abstract We hypothesized that a floating trawl bridle that does not contact the seabed would reduce the herding of fish, especially bottom dwelling flounders, and thus reduce bycatch of these fish in shrimp trawls. We further hypothesized that, due to the non-herding nature of northern shrimp (Pandalus borealis), the use of an off-bottom floating bridle would not reduce shrimp catch. These hypotheses were tested in the field by comparing a trawl with regular bottom-tendering wire bridles and the same trawl with floating synthetic bridles in the Gulf of Maine northern shrimp fishery. As expected, no statistically significant differences in catch rates and size were found for the targeted northern shrimp (146.3 ± 10.58 kg h−1 control vs. 140.8 ± 9.35 kg h−1, p = 0.13). Total finfish bycatch was reduced by 14.9%, and the difference was statistically different (p = 0.01). The most important reduction was the catch of juvenile American plaice (Hippoglossoides platessoides) with a significant reduction of 20.0% (p = 0.01). For witch flounder (Glyptocephalus cynoglossus), a reduction of 19.3% was found, but it was not statistically significant (p = 0.14). The reduction of Acadian redfish (Sebastes fasciatus) (by 28.0%, p = 0.02) was also statistically different. Catch of targeted silver hake (Merluccius bilinearis) was reduced by 10.8%, but the difference was only marginally significant (p = 0.07). An analysis of length frequencies for the targeted shrimp and major bycatch species revealed no size-related selection between the gears with regular bridles and floating bridles. The reductions in flounder bycatch indicate reduced herding of benthic species when the bridles are kept off bottom. This easy modification may be readily adopted in the northern shrimp fisheries in the North Atlantic, and can also possibly be applied in other shrimp and prawn fisheries with further experimentation.

Multiple-Frequency Acoustic Backscattering and Zooplankton Aggregations in the Inner Scotian Shelf Basins

1991 ◽  
Vol 48 (3) ◽  
pp. 340-355 ◽  
Author(s):  
N. A. Cochrane ◽  
D. Sameoto ◽  
A. W. Herman ◽  
J. Neilson
Keyword(s):  
Target Strength ◽  
Scotian Shelf ◽  
Migration Patterns ◽  
Acoustic Backscattering ◽  
Large Populations ◽  
Order Of Magnitude ◽  
Silver Hake ◽  
Merluccius Bilinearis ◽  
Domain Dependence

Acoustic backscatter observations at 12, 50, and 200 kHz in the inner Scotian Shelf basins reveal large populations of silver hake (Merluccius bilinearis) and its principal prey, the euphausiid Meganyctiphanes norvegica. Multichannel sonar colour imagery facilitates separation of fish from euphausiids and delineation of their separate diurnal migration patterns. Silver hake acoustic abundances are consistent with midwater trawl sampling. Acoustic column densities for mature M. norvegica of approximately 1000/m2 exceed net sampling column densities by over 1 order of magnitude indicating strong net avoidance. Numerical simulation of euphausiid backscattering using a fluid cylinder model and natural distribution of scatterer orientations yields an approximate 20 log L target strength length dependence and little frequency domain dependence in the "geometric" scattering regime. Quantitative interpretation of euphausiid scattering in situ must account for randomness in their orientations.

Variation in the Competitive Abilities of Fishermen and its Influence on the Spatial Distribution of the British Columbia Salmon Troll Fleet

1990 ◽  
Vol 47 (6) ◽  
pp. 1116-1121 ◽  
Author(s):  
M. V. Abrahams ◽  
M. C. Healey
Keyword(s):  
British Columbia ◽  
Ideal Free Distribution ◽  
Fishing Effort ◽  
Catch Rate ◽  
Fish Distribution ◽  
Fish Stocks ◽  
Fishing Vessels ◽  
Catch Rates ◽  
Ideal Free ◽  
The Ideal

We estimated the catch rates of individual fishing vessels within the British Columbia salmon troll fleet from the data of a 7-yr log book program. Catch rates varied considerably among vessels. A portion of the variation could be attributed to environmental variation. However, there were also significant differences in competitive ability among vessels. The top ranked vessels had a catch rate 3.6 times that of the lowest ranked vessels. Top ranked vessels distributed their fishing effort among more fishing areas than bottom ranked vessels, but were also more successful at catching fish when fishing in the same areas as bottom ranked vessels. This information, through an application of the ideal free distribution theory, can be used to develop a model that will describe the expected relationship between vessel distribution, vessel catch rate, and fish distribution, potentially allowing vessel distributions to be used as a tool for assessing fish stocks.

Risk and information use in two competing fleets: Russian and Cuban exploitation of silver hake (Merluccius bilinearis)

2002 ◽  
Vol 59 (8) ◽  
pp. 1275-1286 ◽  
Author(s):  
D M Gillis ◽  
M A Showell
Keyword(s):  
Soviet Union ◽  
Information Exchange ◽  
Public Information ◽  
Fleet Size ◽  
The Soviet Union ◽  
Catch Rates ◽  
Using Data ◽  
Silver Hake ◽  
Merluccius Bilinearis ◽  
Fish Abundances

Information exchange should influence the ability of individual vessels to exploit fish aggregations, ultimately influencing fishing efficiency. We examined this hypothesis using data from Cuban and Russian vessels pursuing silver hake (Merluccius bilinearis) on the Scotian Shelf from 1989 to 1993. Cuban fleet size and organization were similar among the years, while the Russian fleet decreased in size and became profit driven during this time. Changing fish abundances prevent direct comparisons of fishing success between years, but the relative performance of the nations provided a basis for interannual comparison of fishing success. The risk of gear damage during a trawl differed between the nations in the years studied. From 1989 to 1992, vessel performance improved after a move of over 20 nautical miles, but this trend was absent from the 1993 data. When movements were separated into potential tactics, moving to an area where other ships were fishing was most common, suggesting the use of public information. Russian vessels were significantly less mobile than Cubans immediately following the dissolution of the Soviet Union and their seasonal catch rates were typically lower. In the following year, Russians were more mobile than Cubans and their seasonal performance was comparable.

Storage Life of Refrozen Silver Hake (Merluccius bilinearis) Processed as Fillets am Minced Flesh from Thawed, Stored, Round-Frozen Fish

1977 ◽  
Vol 34 (12) ◽  
pp. 2369-2373 ◽  
Author(s):  
Doris Fraser Hiltz ◽  
D. H. North ◽  
Barbara Smith Lall ◽  
R. A. Keith
Keyword(s):  
Key Words ◽  
Frozen Storage ◽  
Storage Life ◽  
Freeze Thaw ◽  
Acceptable Quality ◽  
Frozen Fish ◽  
Silver Hake ◽  
Merluccius Bilinearis ◽  
Protein Extractability

Refrozen silver hake (Merluccius bilinearis), processed as fillets and minced flesh after thawing of stored round fish that had been frozen within 14 h of capture, underwent rapid deterioration during storage at −18 °C compared with once-frozen control materials from the same lot of fish. The estimated maximum storage life of silver hake refrozen as fillets after 3 and 6 mo storage of the round fish at −25 °C was reduced to about 4.5 and 1 mo, respectively, from 10 mo for once-frozen control fillets. Quality of the refrozen materials immediately after thawing and refreezing was similar to that of the round-frozen fish, except after 6 mo, where some initial deterioration occurred, particularly in minced flesh. Minced flesh was more unstable in frozen storage than fillets. In all once- and twice-frozen materials, formation of dimethylamine occurred concomitantly with decrease in protein extractability. Round-frozen fish underwent no loss in protein extractability during 6 mo storage at −25 °C, but some lipid hydrolysis occurred. These results suggest that the freeze–thaw–refreeze process as applied to silver hake will yield a final product of acceptable quality provided that storage of the round fish does not exceed 3–4 mo and that the refrozen materials are marketed within a month after processing. Key words: silver hake, Merluccius bilinearis, refrozen storage, dimethylamine, minced flesh

Sign in / Sign up

Export Citation Format

Share Document